Gold-catalysed cycloisomerisations of ketoalkynes

Abstract

The direct cyclisation between alkynes and ketones was described by Conia in 1964. Under high temperatures (150-650 °C), alkynyl and alkenyl ketones were converted into carbocycles, bis-fused carbocycles and spiro compounds by a pericyclic ene-type reaction. However, the use of elevated temperatures limits its applications to thermally robust molecules. Since the original report, a significant amount of effort has been made to develop alternative approaches under mild conditions. These methods employ activated methylenes, frozen enol equivalents or enamine intermediates as nucleophiles in the presence of a Lewis acid (Hg, W, Pt, Au) to activate the unsaturated moiety. Although, synthetically useful, these processes are limited by the necessity to use a preformed enol or a co-catalyst, which involves additional synthetic steps and reagents.

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